Discordant Effect of IFN-β1a Therapy on Anti-IFN Antibodies and Thyroid Disease Development in Patients with Multiple Sclerosis

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Abstract
Interferon-β1b (IFN-β1b) therapy is associated with a relatively high risk of developing thyroid disease. IFN-β1a is regarded as less immunogenic than IFN-β1b because of its structural homology to natural IFN-β. We assessed the effect of 1 year of IFN-β1a treatment on thyroid function and autoimmunity in 14 multiple sclerosis (MS) patients. The results were compared with those obtained in a series of 31 MS patients treated with IFN-β1b. The prevalence of positive binding antibody (BAb) titer and neutralizing (NAb) anti-IFN antibody titer in the two groups was also assessed. The BAb and NAb positivity rate in IFN-β1a-treated patients was significantly lower than in the group submitted to IFN-β1b therapy (7% vs. 84% and 0% vs. 30%, respectively). Although the incidence of thyroid dysfunction was slightly higher in IFN-β1b-treated patients than in those undergoing IFN-β1a treatment (33% vs. 23%, respectively), it did not reach statistical significance. Thyroid disease was unrelated to the presence of positive serum BAb or NAb titer in both the group undergoing IFN-β1a therapy and in that treated with IFN-β1b. In both groups, thyroid disease developed mostly in women (71%) against a background of preexisting thyroiditis and a diffuse hypoechoic ultrasound thyroid pattern (80%). IFN-β1a treatment was associated with a significantly lower prevalence of both BAb and NAb-positive titers than was IFN-β1b. Conversely, thyroid disease was similar and unrelated to the presence of positive anti-IFN-β antibody titer. Therefore, routine thyroid assessment may be advised during IFN-β1a treatment, especially in patients with preexisting thyroiditis.